Today, Global Positioning System (GPS) satellites are used by land based communication systems for synchronization between base sites. Such synchronization requires the reception of at least one GPS satellite signal by each base site within the communication system. However, simply receiving a single GPS satellite signal is not enough to ensure that the base site is synchronized, since the GPS satellite signal received may be unreliable.
In order to ensure reliability of a GPS satellite signal used for synchronization, GPS Real-time Autonomous Integrity Monitor (RAIM) is used. RAIM, as described in the IEEE article "Prediction of the Time Accuracy and Integrity of GPS Timing", requires that two or more GPS satellite signals be simultaneously received, however. This requirement is a significant constraint when choosing a location for a base site. For example, locations with nearby man-made structures or local geographical features that prevent a base site from simultaneously receiving the two or more GPS satellites cannot be chosen.
Although a single GPS signal may be used to synchronize communications, in order to insure that the single GPS signal is itself reliable, base sites must be located where at least three GPS signals can be received. There is a need, therefore, for an apparatus and method for determining the reliability of a single GPS signal at a base site without requiring the reception of additional GPS signals by the base site.